The invention is generally related to providing multiple semiconductors in a common package, and, in particular to multi-chip modules (MCM) that includes an integrated circuit (IC) and one or more power devices, especially a half-bridge circuit with a driver IC and high side and low side power mosfets.
In U.S. Pat. No. 7,915,721, a MCM is shown with an IC and two power mosfets packaged as a module. The IC is formed on a die of semiconductor material which is attached to a central die pad of a leadframe. Very thin wire bonds connect the bond pads of the IC to external and internal leads or to the power mosfets. The mosfets are flip chip attached to leadframes and have clips that selectively connect terminals of the mosfets to the IC and to internal and external leads.
The above reference demonstrates the two types of assembly techniques common in the semiconductor industry: wire bonding and flip chip attachment. Wire bonding generally requires larger package sizes since the wire bonds need room to loop wire from the bond pads on the IC to the leads of the leadframe. As the IC becomes more complex, it tends to have more bond pads for input, output and internal connections to other devices.
Although the technology of wire bonding has overcome many obstacles, nevertheless wire bonding has a number of disadvantages and drawbacks. The designer must leave physical space in the package to allow room for the bonding equipment to attach one of each wire to a bond pad, loop the wire, and attach the other end of the wire to the leads. In many cases the external leads are distributed around the periphery of the package, thereby requiring a package outline that is substantially greater than the size of the IC die. Even with all the improvements in wire bonding, there are still risks of displacement in X, Y and Z axis during assembly. Stacked devices with wire bonds are prone to misalignment. The wire bonds themselves are subject to a number of potential failures including ball/wedge bond lifting, shorting, wire breaking, voids in bonds and contaminants. Each wire bond may fail at any one of three points: the bond pad, the lead and along the length of the wire and any one failure will result in the loss of the entire die even if the die passed its electrical tests.
Other assembly techniques provide packages that have very small profiles. With flip chip assembly, balls, pillars or bumps are deposited on the contact terminals of chips. The balls, pillars, or bumps are attached to pads or leads in a single operation where the balls, pillars or bumps are soldered to the leads. Where a single mosfet or multiple mosfets are all flip chip assembled and encapsulated with an insulating resin, the resulting package may be relatively small, approaching the actual scale of the chips themselves. Since power mosfets have only three terminals (source, gate and drain) it is relatively simple to flip chip assemble mosfet and make a chip scale package. However, when a MCM includes an IC, the multiple wire bonds required to assemble the IC will result in a relatively large size package in order to accommodate the wire bonded IC, such as the one shown in U.S. Pat. No. 7,915,721.